U.S. Pat. No. 4,213,661 entitled "Bearing Support Structure Combining Fluid Damping and Spring Damping Apparatus" granted to R. A. Marmol on July 22, 1980 and assigned to the same assignee as this patent application, typifies a fluid damper that is constructed with a plurality of arcuate beams that are mounted end-to-end to surround the bearing. As disclosed in that patent, the bearing is free to move orbitally about its annular cavity. This motion is transmitted to the fluid in the damper which in turn generates a hydrodynamic pressure which resists further displacement and effectively dampens the vibratory motions. Curved beam dampers, while efficacious for damping high loads are costly to manufacture, install and maintain. Obviously, because the individual segments must be manufactured with close tolerances and care must be used in assembling the parts, they are considered complex and impose a potential wear problem on multiple parts. The curved beams which are a series of segmented parts are supported so as to also have spring-like characteristics.
Another method of obtaining the mechanical spring is to incorporate a separate mechanical spring either mounted in parallel to or in series with the fluid damper. An example of a mechanical spring and fluid damper configuration is disclosed in U.S. Pat. No. 4,457,667 granted to W. S. Seiburt and W. B. Hill on July 3, 1984 and assigned to United Technologies Corporation, the assignee of this patent application, which is incorporated herein by reference. As disclosed therein, the spring attaches to the inner support member defining the fluid damper and the bearing compartment housing and like the other mechanical spring devices serves to provide additional spring rate for a high unbalance condition as well as to center the rotor on engine shut-down. The spring consists of a plurality of rods that are circumferentially disposed around the fluid damper which, obviously, is a complex assembly. Like the heretofore known fluid damper, the springs consist of a relatively large number of parts that require close tolerances particularly to maintain the desired spring rate which consequently compound the problems of installation and wear.
I have found that I can obviate the problems enumerated in the above by providing a single piece full hoop fluid damper and spring combination that is considerably simpler than heretofore designs.